It is well known that petroleum resins are prepared by thermal polymerization of feeds obtained from petroleum refining, which contain mainly cyclopentadiene, dicyclopentadiene and alkyl-substituted derivatives of any of those. The polymerization temperature is usually between 200.degree. C. and 350.degree. C. The resulting resin has molecule weight between 200 to 1000 and has a yellow crystalline appearance. It is believed that the reaction process involves two mechanisms, Diel-Alder cycloaddition and free radical propagation. As expected, the final resin is not a single compound but contains many possible molecular structures.
Because of the abundance and availability of petroleum resins, there has been a tendency to use them as additive resin in printing inks. However, these resins have suffered from two generic disadvantages, (i) poor high temperature and UV stability and (ii) low compatibility with polar materials. The instability is due to the unsaturation in the resin. Hydrogenation reactions have been carried out to remove the double bond and simultaneously minimize the color. On the other hand, to improve the compatibility of petroleum resin with basic polymers, such as polyurethane or with pigments, a polar group is introduced to petroleum resins to enhance intermolecular interaction.
There has been much prior art describing the preparation of polar group containing resins. The best known compound is maleic anhydride modified resin which can be obtained either by direct copolymerization of maleic anhydride and cyclopentadiene derivatives, or by subsequent reaction of petroleum resin with maleic anhydride. However, both processes suffer from contamination and gelation due to insufficient conversion and side reactions. Moreover, those reactions do not substantially reduce the double bond content, so that the thermal stability is not entirely satisfactory.
To introduce hydroxyl and ester groups to petroleum resins, it has been reported to copolymerized dicyclopentadiene with alkyl alcohol, methacryl alcohol, acrylic ester, methacrylic ester, and vinyl ester. However, the cycloaddition products and vinyl co-monomers often have low reactivity, and resulting low level of incorporation. As expected, those materials also suffer from the thermal instability at high temperature due to bonds with unsaturation.
Borane compounds are valuable intermediates in organic synthesis (H. C. Brown, Organic Synthesis Via Borane, Wiley-Interscience, 1975). Many functional groups, such as --NH.sub.2, --OH, --COOH, --COH, etc., can be obtained from a borane moiety under mild conditions. However, the borane group containing petroleum resins are new and the selective hydroboration of the double bond in norbornene is novel, which allows us to obtain thermally stable functional resins with locally well-defined molecular structure.